Dan Rosenberg discovered that insufficient input validation in VLC's processing of Matroska/WebM containers could lead to the execution of arbitrary code.
For the stable distribution (squeeze), this problem has been fixed in version 1.1.3-1squeeze3.
The version of vlc in the oldstable distribution (lenny) is affected by further issues and will be addressed in a followup DSA.
For the unstable distribution (sid), this problem has been fixed in version 1.1.7-1.
We recommend that you upgrade your vlc packages.